There seems to be confusion over just what the chance of rain means in a forecast and now I understand why.
Does a 30-percent chance mean there’s a one-in-three possibility of getting rain? Does it mean one-third of the forecast area will get rain?
I just read a National Weather Service newsletter that explains how it all works. It set my head to spinning. Rain chances are based on a formula where C x A = probability of precipitation.
The C represents how confident the forecaster is rain will fall somewhere. The A represents the percent of the area that will get measurable rain, if at all.
The chance of rain has nothing to do with how much it will rain. If there is a 100-percent chance of rain and only 0.01 of an inch falls, the forecast was correct!
For a more detailed explanation, go to: www.srh.noaa.gov/images/ewx/Spring_09.pdf
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Good post. Most people never knew that, and when I tried to explain the same, I was called out as making it up.
June 3, 2009 at 7:51 p.m.